The present invention relates to a mold used for foam molding a material for a synthetic resin molded foam, particularly, a synthetic resin molded foam having open cells such as a flexible polyurethane foam. This invention also relates to a process of foam molding a material for a synthetic resin molded foam using the mold.
Japanese Utility Model No. Sho 58-60418 discloses a process of producing an interior piece of equipment for a car such as a cushion pad by foam molding a polyurethane foam molding material, characterized in that the pressure in a cavity of a mold is adjusted.
In this process, a lower mold half and a middle mold part are set to form a molding cavity therebetween and an upper mold half is disposed to cover the lower mold half and the middle mold part, and a pressure adjusting chamber is formed between the middle mold part and the upper mold half and vent holes communicating the chamber to the cavity are formed in the middle mold part, whereby air in the cavity is evacuated to the chamber through the vent holes.
The process disclosed in the above document, however, has a disadvantage. When a pad having a relatively simple shape is foam molded, an air reservoir occurs in the molded pad near the parting portion, with a result that the percent of defective molded pads is very much increased. The prior art process presents another disadvantage. Since adjustment in pressure between the cavity and the chamber is performed only through the vent holes, the size and the number of the vent holes must be increased, and consequently the air is non-uniformly evacuated from the cavity to the chamber. This results in an uneven distribution of foamed cells of the product, and also requires a laborious work of cleaning burrs caught in the vent holes after molding.
Japanese Patent Publication No. Hei 7-102583 discloses a process for molding a material for a polyurethane foam, comprising the steps of depressurizing the interior of a cavity of a mold, and pouring in the cavity a polyurethane foam molding material obtained by mixing 100 parts by weight of a polyol component and 0.1-0.6 part by weight of water as a foaming component and foaming it thereby filling the cavity with the fluidized material. The process, however, has a disadvantage. In the step of depressurizing the interior of the cavity of the mold, the interior of the cavity is evacuated through a gap between PL (parting line) surfaces formed when at least two-divided mold portions of the mold are closed. Specifically, the neighborhoods of the PL surfaces of the mold are surrounded by a space portion and the interior of the cavity is evacuated through the gap between the PL surfaces by depressurizing the space portion. As a result, burrs tend to be formed in the gap between the PL surfaces.